If `reflection_scope.where_clause` is not empty, `through_scope` should
be joined the source association. But if the through association doesn't
have explicit `:source`, `options[:source]` will be nil and
`scope.includes_values` will also be empty. It should use
`source_reflection.name` rather than `options[:source]`.
Fixed by a26cff3.
Fixes#11078.
Fixes#26129.
Closes#14312.
Closes#29155.
Closes#29841.